Spindle unit with a spindle supported by prestressed antifraction bearings

ABSTRACT

The invention concerns a spindle unit with a spindle, a casing, antifriction bearings that are prestressed and support the spindles on two places at a distance from each other in a casing, and a centrifugal regulator, which reduces the prestress on the antifriction bearings as the rotational speed increases, as a result of which the centrifugal regulator is produced as a springy, axially expanding bush with resilient arch-like parts between two compression components and each mass on the arch-like parts.

The invention concerns a spindle unit with a spindle, a casing,antifriction bearings that are prestressed and support the spindles ontwo places at a distance from each other in a casing, and a centrifugalregulator, which reduces the prestress on the antifriction bearings asthe rotational speed increases, as a result of which the centrifugalregulator is produced as a springy, axially expanding bush withresilient arch-like parts between two compression components and eachmass on the arch-like parts.

Such a spindle device is known from DE-U-94 04 249. Such spindle unitsare used, for example, in machine-tool construction. With such a spindledevice the prestress of the spindle antifriction bearings can be reducedduring high-speed machining. The spindle units can also be used insimilar structural components of various machines. The regulator used inthe known construction guarantees the correct coordination of therotational speed of the spindle and the prestress of the antifrictionbearing, which is, practically speaking, congruent to the recommendedcoordination of the rotational speed of the spindle and the prestress ofthe antifriction bearing (cf., e.g., the 3700 T catalog: SKF precisionbearing, pg. 64, reg. 47150001987-03, printed in the Republic of Germanyby Weppert GmbH & Co. KG). In comparison with the traditionalconstructions with hydraulic control of the prestress of the spindlebearing, as is described, e.g., in the journal Konstruktion (no. 44, p.A20, 1992 for HSC spindles), the spindle unit is constructed in asimpler fashion in accordance with the above German working model.

By virtue of the fact that the variation of the prestress of the spindlebearing is dependent on the displacement of the inner rotating bearingrings, corrosion caused by friction can occur on the outside surface ofthe spindle; cf., e.g., Tribology Handbook, ed. M. J. Neale, London:Butterworth, 1973, chap. E7. In the case of the known constructionnamed, the regulator with its resilient arch-like parts and the massesarranged on them are located between the bearings for the spindle.

The problem the invention tries to solve is to improve a spindle unit ofthe type under discussion so that spindle corrosion caused by thedisplacement of the inner bearing rings with respect to the spindle isavoided, in turn increasing the longevity of the spindle unit.

According to the invention this will be obtained when the regulator issupported by regulator antifriction bearings on its two ends on a casingof the spindle unit; when the regulator does not touch the spindle; whenthe outer nonrotating rings of the regulator antifriction bearings pressagainst the outer rings of the spindle bearings; and when the regulatoris set in rotation with the aid of a springy component, which has a highresistance to rotation and a low resistance to bending, allowing for theaxial movement of the regulator with respect to the spindle, as a resultof which the springy component is firmly connected to the spindle andregulator.

The regulator consequently acts on the outer ring and is positioned soit can move axially to the spindle. In so doing the danger of acorrosion of the spindle is eliminated because the thrust rings of theregulator displaces the outer nonrotating rings of the spindle bearingswhile the prestress is being regulated.

The regulator is located, as is usual, between the spindle bearings andrequires only a little space. It is, however, also possible to mount theregulator outside the spindle, in which case existing spindle units canbe converted. For this purpose the regulator is mounted outside thesection on each of whose ends the spindle bearings are located, in whichcase the outline of the arch of the resilient parts of the regulator hasa concave form. With such a construction only minimal changes need to bemade in the construction of existing spindle units.

The invention is more clearly illustrated in two working examples withthe use of drawings, in which

FIG. 1 represents a longitudinal section through a first working exampleof a spindle unit according to the invention;

FIG. 2 represents a cut along A-B in FIG. 1;

FIG. 3 represents a longitudinal cut through a second working example ofa spindle unit according to the invention with a regulator placedoutside the spindle;

FIG. 4 represents a cut along C-D in FIG. 3.

A spindle unit has a casing (1) with spindle bearings (2, 3, and 4) fora spindle (5). To produce a basic prestress and the regulation of theprestress, a centrifugal regulator is foreseen, which consists ofresilient parts (6), masses (7) arranged on them, and thrust rings (8and 9). The resilient parts (6), the masses (7), and the thrust rings(8, 9) are produced as one part. The outline of the arch of the elasticparts (6) has a convex form. The regulator is supported on both of itsends by regulator antifriction bearings (10, 11) on the casing (1) ofthe spindle unit. An annular membrane (12), which has a high resistanceto rotation and a low resistance to bending, is firmly connected to aspacer tube (13) and the thrust ring (9) of the regulator. The spacertube (13) is mounted between the inner ring of the spindle bearing (4)and an extension of the spindle (5) and connects the regulator and thespindle (5) via the membrane (12). The thickness of the spacer tube (13)also determines the maximum magnitude of the prestress of the spindlebearings (2, 3, and 4)--i.e., in other words, the magnitude of the basicprestress. The distance ring (14) is mounted between the outer rings ofthe spindle bearing (4) and the regulator antifriction bearings (11);the outside ring of the regulator antifriction bearing (10) is pressedagainst a back extension of the casing (1). A face of a nut (15) on theend of the spindle is pressed against the inner ring of the spindlebearing (4). The outer rings of the spindle bearing (2 and 3) aremounted between a front extension of the casing (1) and a top (16).

The regulation of the bearing prestress is carried out as follows. Toproduce the basic prestress the nut (15) is screwed into the threads ofspindle (5). The face of the nut (15) is pressed against the inner ringof the spindle bearing (4) and through the spindle bearing (4), thedistance ring (14), and the regulator antifriction bearing (11) on thethrust ring (9), by means of which the arches of the resilient parts (6)are bent and the spindle bearings (2, 3, and 4) are opened for the basicprestress. The prestress of the spindle bearing (4), i.e., thedisplacement of its inner rings with respect to the outer rings, isincreased until the spacer tube (13) comes in contact with the extensionof the spindle. This goes for the spindle bearings 2 and 3 as well, forthe entire spindle, including the inner rings of the spindle bearings 2and 3, shift back at the same time when the basic prestress is produced.

When the spindle (5) rotates, the regulator is also set in rotation bythe membrane (12). The inertia masses (7) generate centrifugal forces,and these produce horizontal constraining forces on the sites where thebent parts (6) are anchored in the thrust rings (8 and 9), consequentlyreducing the prestress.

Because the annular membrane (12) has a low resistance to bending, thedisplacements of the thrust rings (9) do not generate any displacementsof the spindle (5) by the membrane (12) while the prestress is beingregulated. When the prestress is reduced by increasing the spindle'srotational speed, a displacement of the inner rings of the spindlebearings (2, 3, and 4) or the spacer tube (13) with respect to thespindle (5) also does not occur. Instead, the entire spindle (5),including the inner rings of the spindle bearings and the spacer tube(13), shift forward at the same time. The variation of the bearingprestress is only connected with a displacement of the outer nonrotatingrings of the spindle bearing (4) and the regulator bearings (10 and 11),as well as the distance ring (14) with respect to the casing (1). Inthis way the danger of spindle corrosion is eliminated.

In FIGS. 3 and 4 a second working example of a spindle unit isrepresented, in which the regulator and its regulator bearings (10 and11) lie outside the section on whose ends the spindle bearing islocated. It is housed in an additional casing (21). The referencenumbers 1 to 11 in FIGS. 3 and 4 designate parts that are the same asthose referenced in FIGS. 1 and 2; the reference number (19) in FIG. 3is a top of the spindle unit and corresponds in this regard to the top(16) in FIG. 1.

In this working example the outline of the arch of the elastic parts (6)has a concave form. The casing (21) is firmly connected to the casing(1). The spindle unit contains cup springs (22, 23), which are mountedbetween the outer ring of the spindle bearing and an extension of thecasing (1). An annular membrane (24) is firmly connected to a nut (25)and a thrust ring (9) of the regulator. The nut (25) runs on the spindle(5); and the face of the nut is pressed against the inner ring of thespindle bearing (4). A distance ring (17) is mounted between the innerring of the spindle bearing (4) and the extension of the spindle (5),whose thickness determines the maximum magnitude of the prestress of thespindle bearings (2, 3, and 4). A spacer tube (18) is mounted betweenthe outer rings of the spindle bearing (4) and the regulator bearing(10). The annular extension of a back top (20) of the casing (21)presses against the outer ring (11). The thickness of this annularextension determines the preliminary prestress of the deformable part(6). To produce the basic prestress the nut (25) is screwed onto thethreaded part of the spindle (5). The face of the nut (5) is pressedagainst the inner ring of the spindle bearing (4) and bends the cupsprings (22 and 23) while the nut continues to be screwed in, as aresult of which the basic prestress of the spindle bearings (2, 3, and4) is adjusted. The prestress of the spindle bearings (2, 3, and 4) isincreased until the distance ring (17) comes in contact with theextension of the spindle (5).

While the spindle (5) is rotated, the regulator is also set in rotationby the membrane (24). Because the regulator is placed outside thesection on whose end each of the spindle bearings are located, theconstraining forces that arise during rotation bear in a direction thatruns contrary to that shown in the first working example in FIGS. 1 and2. For this reason the outline of the arch of the resilient parts (6)has a concave form. In contrast to the first working example accordingto FIGS. 1 and 2, the prestress of the regulator bearings (10, 11)increases as the prestress of the spindle bearings (2, 3, and 4)decreases. By virtue of the fact that the regulator bearings (10 and 11)can have a smaller diameter than the spindle bearings (2, 3, and 4), itis possible to carry out a desired limitation of the coordinationbetween the rotational speed and prestress for both the spindle bearings2, 3, and 4 and the regulator bearings 10 and 11 if one uses the bearingmodel CD, series 719, for the spindle bearing and model ACD, series 70or 72 (with a relatively higher prestress magnitude (class A, B, C) andrelatively lower rotation speed limits) for the regulator bearing. Thiscan mean, e.g., the following bearings, which are listed on pages 62,72, and 74 of the above-mentioned catalog:

bearing 71920 CD, bore 100 mm prestress in accordance with class A, B, C230, 460. 920 N rotational speed limit in connection with the greaselubrication 8500 U/min

bearing 7012 ACD, bore 60 mm prestress in accordance with class A, B, C240. 480. 960 N rotational speed limit in connection with the greaselubrication 13000 U/min.

From these data one can see that the reduction of the prestress of thespindle bearing of a maximum magnitude in accordance with class C at arotational speed of zero to a minimum magnitude in accordance with toclass A at a maximum rotational speed corresponding to the speed limitgenerates an admissible increase in the prestress of the regulatorbearing.

In this way the proposed construction eliminates the danger of spindlecorrosion and simplifies the use of the centrifugal regulator.

I claim:
 1. Spindle unit, which consists of the following components:aspindle (5), a casing (1), antifriction bearings (2, 3, 4), whichsupport the spindle on two sites at a distance from one another in acasing and which are prestressed, a centrifugal regulator (6, 7, 8, 9)that reduces the prestress on the antifriction bearings as therotational speed of the spindle increases, and in so doing, thecentrifugal regulator is produced as a springy, axially expanding bushwith resilient arch-like parts (6) between two compression components(8, 9) and the masses (7) on the arch-like parts, characterized by thefact thata) the regulator is supported by regulator antifrictionbearings (10, 11) on both of its ends on a casing (1, 21); b) theregulator does not touch the spindle (5); c) the outer nonrotating ringsof the regulator antifriction bearings (10, 11) press against the outerrings of the spindle bearing (4); and d) the regulator is set inrotation with the aid of a springy component (12, 24), which has a highresistance to rotation and a low resistance to bending, allowing for anaxial movement of the regulator with respect to the spindle, in whichcase the springy component is firmly connected to the spindle and theregulator.
 2. Spindle unit according to claim 1, characterized by thefact that the regulator (6, 7, 8, 9) is mounted outside the section onwhose ends the spindle bearings (2, 3, 4) are located, as a result ofwhich the outline of the arch of the resilient parts (6) of theregulator has a concave form.
 3. Spindle unit according to claim 2,characterized by the fact that the regulator is placed in a separatecasing (21).
 4. Spindle unit according to one of the previous claims,characterized by the fact that the resilient parts (6), the masses (7),and the bearing rings (8, 9) together make up a single part.